A study of the effects of specific functional group reagents and affinity-labeling reagents on the activity of catechol-O-methyl- transferase (COMT), an enzyme important in the metabolism of epinephrine and norepinephrine, will be undertaken in an attempt to elucidate the nature of the amino acid residues present at the active site. Functional group reagents specific for sulfhydryl and amino groups will be of particular interest. Two classes of affinity labeling reagents for this enzyme will be studied with particular emphasis being placed on determination of the amino acid residues being modified during these reactions. Also of interest will be the purification and characterization of the soluble and membrane-bound forms of COMT isolated from rat brain and heart. The rat liver enzyme has been extensively studied in our laboratory and differences between liver COMT and heart and brain COMT will be of particular interest. This basic type of biochemical information will be used for the design of specific inhibitors of this metabolic pathway.